Abstract

Microbial ecology is the younger sub-discipline of ecology, but its scope is clearlyimmense. Microorganisms’ specificities represent a major hurdle to the applicationof traditional ecological approaches. Recently, the opportunity to apply ecologicalprinciples to microorganisms was suggested. It is assumed that existing principlesmight apply, but that they are probably also driven by specific principles.Microorganisms have varying metabolic abilities and are classified as generalists orspecialists. We hypothesised that contrasting metabolic properties may drivegenotypic distribution. Model generalist and specialist genera were selected anddistribution patterns along the salinity gradient of the River Colne estuary studied.Two models were studied in detail, Desulfobulbus a versatile sulphate-reducingbacterial (SRB) genus and Methanosaeta, a strict aceticlastic methanogenic archaea(MA). Isolation of Methanosaeta was attempted in order to link phenotypes togenotypic distribution. Two other models were also studied: Methanosarcina themost versatile MA genus and Desulfobacter a metabolically restricted SRB genus.Denaturing gel gradient electrophoresis (DGGE) and clone libraries analyses wereused to determine genotypic distribution patterns.Methanosaeta have proven to be highly recalcitrant to isolation. Adjustments tocommonly used anaerobic culturing methods allowed the obtention of Methanosaetacolonies. In contrast to previous studies, colonies were successfully transferred intoliquid medium, and growth of pure clonal cultures confirmed.Desulfobulbus genotypic distribution pattern was previously shown to be sequentialalong the estuary. Contrastingly, Methanosaeta genotypic distribution pattern wasfound to be monotonic. Furthermore, active genotypes distribution was also foundmonotonic, with an apparent general increase in activity with decreasing salinity.Distribution patterns of the four different genera confirmed this trend. Thegeneralists were both shown to have sequential distribution patterns. Contrastingly,the specialists were both shown to have monotonic distribution patterns.These results confirm the hypothesis that genotypic distribution patterns microbialcommunities structure are strongly driven by microorganisms’ metabolic propertiesand adaptative potential.